It’s a scroll bar swf file that controls a div’s position, not sure why Vimeo did this but it’s cool.
Here’s an example. http://www.vimeo.com/9145294

I think this would be a cool component to build. A friend wanted me to build this for him but I don’t have time right now. I’m pretty sure that this could possibly be a featured item and thought it might be cool for AD to have this.